Decarboxylation of 2-hydroxy-3-carboxyl pyrazine



Patented Aug. 16, 1949 DECARBOXYLATION or z-nrmtoxr-sl -CARBOXYL PYRAZINE John Weijlard, Westfield, and Max Tishler, Rahway, N. J assignors to Merck & 00., Inc., Rahway, N. J a corporation of New Jersey No Drawing. Original applications September 18, 1943, Serial Nos. 502,967 and 502,969. Divided and this application April 25, 1946, Serial No.

. 664,978 3 Claims. 1

This application is a division'of our co-pending applications Serial Nos. 502,967 and 502,969, now abandoned, both filed on September 18, 1943. This invention relates to processes for the production of pyrazine derivatives, and more particularly' it relates to the production of such derivatives from correspondingpoly-nuclear compounds containing a lumazine nucleus.

The pyrazine derivatives with which the present invention is concerned are difficult to prepare by processes heretofore available. The present invention is of great value, therefore, since it permits the preparation of such pyrazine derivatives in good yield; and by simple, economical procedures utilizing readily available and relatively inexpensive starting materials.

The polynuclear compounds which may be utilized as startingmaterials according to our invention are lumazine, substituted lumazines including monoand di-alkyl and mono-and diphenyl-substituted lumazines, and phenanthralumazine. Diphenyl lumaz'ine can be prepared by the process disclosed in the Journal of the Ind. Chem. Society, 14, 627 (1937); and phenanthralumazine can be prepared bythe process disclosed in Berichte, 70, 761 (1937) We have found that the pyrimidine ring in these polynuclear compounds may be hydrolytically split, by treatment thereof with an alkali metal hydroxide, in aqueous solution. Depending upon the conditions employed, the reaction product thus obtained may comprise the alkali metal salts of 2-amino-3-carboxyl pyrazines, 2- hydroxy 3 carboxyl pyrazines, or mixtures thereof.

Within the purview of our invention, and as a specific embodiment thereof, we have found that it is possible; when employinglumazine, to control the reaction so that either the alkali 2 metal salt of 2-amino-3-carboxy1 pyrazine, or th alkali metal salt of 2-hydroxy-3-carboxyl pyrazine is obtained in practically quantitative yield. or in substantially preponderant amounts. According to our invention, the substantially selective production of either the alkali metal salt of 2-amino-3 carboxyl pyrazine, or Z-hydroxy-3- carboxyl pyrazine, is achieved by controlling the amount of alkali metal hydroxide employed in the reaction. Generally speaking, when an excess of alkali metal hydroxide is reacted with the polynuclear compound, preponderant quantities of the alkali metal salt of 2-hydroxy-3-carboxyl pyrazine are produced, with correspondingly diminished quantities of the 2-amino-3-carboxyl pyrazine compound. Our invention, then, further comprises the determination of optimum conditions'for the substantially selective production of either alkali metal salts of 2-amino-3- carboxyl pyrazine, or of 2-hydroxy-3-carboxyl pyrazine.

The amount of alkali metal hydroxide to' be used for the preferred production of the alkali metal salt of 2-amino-3-carboxyl pyrazine is preferably in the neighborhood of from 1 to 3 mols of. alkali metal hydroxide to one mol of 111- mazine. Quantities of alkali metal hydroxide substantially-in excess of 1-3 mols to one mol of lumazine tend to favor the production of lar amount of the alkali-metal salt of 2-hydroxy-3- carboxyl pyrazine.

Table I illustrates the results obtained by reacting one molof lumazine with varying quantitles of sodium hydroxide, in aqueous solution, under varying conditions. The table shows the yield of crude 2-amino-3-carboxyl pyrazine, and also the yield of crude and pure 2-aminopyrazine, after decarboxylation, as well as the overall yield on the basis of lumazine.

TABLE I a. 25 a. 25 3. 25 a. 25 a. 11 s. 11 2. s2 2. 00 2. 25 4 moles moles moles moles moles moles moles moles moles moles NaOH NaOH, NaOH, NaOH, NaOH, NaOH, NaOH NaOH, NaOH, NaOH, 1 15111 24 i 21 1115., 15-18 1115 11 1115., .9 2115., 2 1115., 2 1115., 2 1115., s 1115., 4 1115., 170 170 0., 170 0., 170 0., 170 0., 170 0., 150 0., 170 0., 170 0., 170 0., Bomb Bomb Bomb Bomb Bomb Bomb BQmb Bomb Bomb Bomb 9% 2111111 10 11111 11 11111 12 11111 71 11111 12 11111 22 11111 at, 11111 31 11111 210 192-194 l92194 191-193 l2l94 198 198 1 85.3 87.4 80.37, 85.37, 93.57, 9:1.57, 92.97, 92.17, 88.87, P 1: 1 11% 00% 1%? M. 171)? M. R115 M. 1.5 M. 1. 118- M. P. 118- M. P. i18- M. P. f10 M. P."11s- 9 [7 120 120 120 7 7 120 Pure 1111111111 7.5 50.57, 51.17, 62.5%, .8 11, 0.4 Pyrazine." I? 1V1. l P, P. 1' P. L 1 118120 118 -120 118120 1181 20 113--120 l18120[ 7, 01111211 Yield 0.87, 41.47;, 38.0% 40. 3% 10.97;, 80.6% 79.07;, 07.3% 00.0% 75.27;,

on Basis Lumaziue.

As will be observed from thetstn'tfi tbtinitm amount of sodium hydroxide to be employed the production of best yields'o'i the-*sodium-fsalt of 2-amino-3-carboxy1 pyrazin'e from lumaz-in'e is about 2.8 mols per mol of 11111191211111. 25 11111 ratio of sodium hydroxide to lumaai increased, the yield of the] amino carboxyl pyrazine salt is correspondingly? d1 However, even at 4 mols of sodium hydroxide to one mol of lumazine, some sodium sa1t 111:"-2"-.-.

amino-3-carboxyl pyrazine is obtained, although e r cti n re inct com r ses a re er amquntof the sodium salt of 2-hydroxy-3-carb'cxyl pyrazine. j

In the case. of jthe substitutedglumazines, which arejmore resistant to-"hyd-rolytic splitting, larger amounts of alkali metal hydroxide are required forthemroduction of "both the corresponding alkail'i metal salt of the 2-amino 3-carboxyl pyrazineand the- 2,.hydroxy- 3-'carboxyl pyrazines, generally in excess 0153 mols of alkali metal hydroxide one mol ofisubstituted lumazine being required for. the producti, on*of.- the alkali metal salt of the 2=amino 3-carboxyl -pyrazine. Prefe'rre'd conditions for "the treatment of ;such sub Stituted. lumazines; according-rte our invention, Willlbe apparent from the specific examples given "The hydrolytic splitting ofthe-pyrimidine "ring of polynuclear compounds containing the lumen- Zine nucleus, according to our invention, may be carried out at atmospheric pressure, or atrincreased'='pressure. The temperatureand time-of- 1'5211'1111110011111110115 Willvary depending upon the pressure employed. 7 1 After. hydrolytic' splitting oft the pyrimidine ring--has;been' effected; the- 111219111011 mixture containing'jthe"a;lkalii metal salts 'of'the 21-amino and/or "2-hydroxy-3 carboxy1-pyrazines may be worked-upin"any"suitable 1111111111111. The free acids: 11191 1 be recovered by adjusting the: pHz'of the reaction mixture to 2-3, and'collectin'gthe crystalline' ma'terial obtained; It -2150 possible to 'obtain "the free acids 'conve'rting' thea'lkali met'alisalt to a barium salt, and then acidulating 21112011115115; 511511111151011 0151111111121111111 salt, Will a'p'pear from the various. examples given h'ereinf' 1 I "The following exampl'es' 11111111911111111111110111 carrying out the present'inventi'on, but'it is 10 b 1111;111:51001111121 these examples are given by 25 way of illustration and not of limitation.

(EXAMPLE I 'l-TytiiatedJuEnaZi-rie, corresponding to 20 gms. of anhydrous material, is added to a solution of 11- gins. of 5 1 11 11 hydroxide in 80 cc. of Water, and, themixture. is: heated in a steel bomb for eight hours at 170* C. The reaction mixture is acidulat'ed with hydrochloric acid to pH 2.5, and chilled to 2 C. 2-afiiino-3-carboxy1 pyrazine crystallizes out. The crystals-are; collected'and Washed with icewater. Yield, 15.85 gins; M. P. 198C? This product may be further pnrified by dissolving it boiling -water,; adjuting the pI-Lto 11-11 1- 11019 11 2 19 a id 09991 1 112 filtering chlling and washing and drying the crystals 111115 11111911111111. 'Mjrj. 2013'. rem

:3 of crude -7-methy1 :lumazine: are added toa solution of 6 ;gms.- of sodium hydroxide 11 30 01 219119 19 h i tur iis b d under r u 1.50 9 61.- Th 1 15 1 11 1 1 th 2 Q Q cc. of 11 111 neutralized, with hydrochloric acid, and 111 115 1 1111 11'1111i6111a'11111 10011501 30% barium chloride "5 11111511 1115111111110, and the 111111111112 150111111111 at 2C. 16121111111012 110111 11101101120100 o'nfa filter, 112 111111 V 2.111101 11111111 va'e'uo'; yield, 2.50

The "111 f 'in"2 00j cc."of I I 10%hyd 0111611 20102111200110, and 11 11 .jmixture is lieat ed'itdboililig. 111111121111- 102111 11 9 79.12 0 921he11o11111 fiitereu'tnn 1111111110 212 09111121100111 121101115. 2-amino-3 carboxy1-fi -irietliyl f pyrazine crystall"e's;out. '-The stal ar '1'1 11511'111w1 11- 11e111'1e1 1 1 111, 9 2 amino-3-carboxyl- 1 EXAMBLEMIHM I *3 1 -5. 11re11'1u1 "dim tnyi iamzme 91111 12100- gd t eajsoiution 016 {sodium-1131011111101 111 30 001111 waterj'and the 11111111111115 boiled 11 10111 reflux for hours. The mixture is worked'up 111 aeeoraaneewit11 the procedured escribed in Examples; Yiel' 9 "1111110911 1111111 salt 101 0 3- 0 oxyl s, diinethyr -pyraz'i'ne. From tlie barium- 112111, li-lo g ms.bf-2 211111110 3- m "1'0 off cipitating with acid, etc.

carboxyl-5,6-dimethyl pyrazine are obtained. The product may be further purified by dissolving it in boiling water containing a small quantity of hydrochloric acid, chilling the clear solution, etc. 2-amino-3-carboxyl-5,6-dimethyl pyrazine of M. P. 209-210 0., with decomposition, is thus obtained.

EXAMPLE IV 3 'gms. of crude 6,7-diphenyl lumazine are added to a solution of 6 gms. of sodium hydroxide in 30 cc. of water, and the mixture is boiled under reflux for 35 hours. An oily mass separates; the mass solidifies to a tough lump on cooling. The solution is decanted 011?, and the mass is washed with some ice water and dried in vacuo. Yield, 2.8 gms. of crude sodium salt of 2-amino-3-carboxyl-5,6-diphenyl pyrazine. The sodium salt is dissolved in 30 cc. of warm water, and the barium salt of 2-amino-3-carboxyl-5,6-diphenyl pyrazine is precipitated with barium chloride solution. Yield, 2.57 gms. The barium salt is suspended in 50 cc. of Water, cc. of 10% hydrochloric acid are added, the mixture is heated to 80 C. and a sufficient amount of methanol (200 cc.) is added to dissolve the liberated compound. The hot solution is filtered, and diluted with four volumes of water. 2-amino-3-carboxyl-5,6-di- 'phenyl pyrazine precipitates in the form of fine crystals, which are washed and dried, Yield, 1.50 gms.; M. P. 188 C.,.with decomposition. The product is dissolved in ethyl ether, the ether insoluble substance is filtered ofi, and the ether solution is concentrated to a small volume. Pe-

troleum ether is added,.and 2-amino-3-carboxyl- 5,6-diphenyl pyrazine precipitates out and is collected on a filter and dried. M. P. 189 C., with decomposition.

EXAMPLE V 9 gms. of phenanthralumazine are added to a solution of 9 gms. of sodium hydroxide in 75 cc. of water, and the mixture is held in a steel bomb at 225-235 C. for 20 hours. The reaction mixture is dissolved in 1000 cc. of boiling water, the solution is treated with some charcoal, filtered,

and acidulated with hydrochloric acid to pH 2.

EXAMPLE VI 2 gms. of 2-amino-3-carboxyl pyrazine are dissolved in 20 cc. of 20% sodium hydroxide solution, and the mixture is heated in a steel bomb at 170 C. for 20 hours. The reaction mixture is diluted with 50 cc. of water and acidulated with hydrochloric acid to pH 2.5-3. 2-hydroxy-3-carboxyl pyrazine is obtained in the form of crystals, which are washed with ice water and dried. Yield, 1.62

gms.; M. P. 218-220 C. This product may be further purified by dissolving it in aqueous sodium bicarbonate solution, decolorizing, re-pre- The white compound thus obtained melts at 218-220 C.

. 122 gms. of sodium hydroxide in 600 cc. of water,

and the mixture is heated at 170 C. for 24 hours .in a bomb. The reaction mixture is diluted with water and acidulated with hydrochloric acid to a pH of 2.5-3. The crystals thus obtained-are collected, washed with ice water, and dried. The 2- hydroxy-3-carboxyl pyrazine thus obtained may be further purified by dissolving it in aqueous sodium bicarbonate solution, decolorizing, re-precipitating with acid, and washing and drying the crystals thus obtained. Yield, 96.4 gms.; 91% of theory; M. P. 218-220 C.

EXAMPLE VIII 22.3 g-ms. of anhydrous 7-methyl lumazine and 24 gms. of sodium hydroxide in cc. of water are heated at -175 C. for 20 hours in a steel bomb. The reaction mixture is made acid with hydrochloric acid (pH 2.5), and chilled to 2" C. for two hours. The crystals are collected and washed with 5x10 cc. of ice water, then dried at 80 C. Yield of 2-amino-3-carboxyl-6-methyl pyrazine, 14.62 gms.; M. P. 211 C.

EXAMPLE IX 2.7 gms. of 6,7-dimethyl lumazine and 2.7 gms. of sodium hydroxide in 25 cc. of water are heated at 170-175 C. in a steel bomb for 20 hours. The reaction mixture is rinsed out of the bomb with 25 cc. of hot water, made acid with hydrochloric acid (pH 2.5), and chilled to 2 C. for two hours. The solid is collected on a filter, Washed with ice water, and dried at 80 C. Yield of Z-amino- 3 carboxyl 5,6 dimethyl pyrazine, 2.15 gms.; M. P. 210 C.

In addition to the sodium hydroxide specifically recited in the foregoing examples, other alkali metal hydroxides as, for instance, potassium hydroxide, may likewise be employed with similar favorable results.

The 2-amino-3-carboxy pyrazines, or 2-hydroxy-S-carboxyl pyrazines, may be converted to the corresponding 2-arnino pyrazines or 2-hydroxy pyrazines by heating the same with substances which are decarboxylating agents therefor.

Solvents which we have found suitable for our purposes are, for example, water, the acetate of diethylene glycol monoethylether, n-butyl phthal ate, sulfuric acid, and liquid petrolatum.

The 2-amino-3-carboxyl pyrazine, or 2-hydroxy-B-carboxyl pyrazine, is heated with the selected solvent, preferably at temperatures between ISO- C. or above. The reaction prod not is then worked up in any suitable manner. For example, it may be decolorized by the addition thereto of a small quantity of a decolorizing black, such as the product known as Darco, for instance, filtered, and the filtrate may then be treated with a solvent such as petroleum ether which precipitates the decarboxylation product.

During the reaction, it is desirableto stir the solution of the 3-carboxyl pyrazine in the selected solvent constantly, and it is preferable to carry out the decarboxylation procedure in equipment provided with a suitable stirring device.

The following examples illustrate methods of carrying out thedecarboxylation procedure.

EXAMPLE X 1 gm. of crude 2-amino-3-carboxyl pyrazine is suspended in 20 cc. of liquid petrolatum. and the mixture is heated at C. for 20 minutes, under fast mechanical stirring. The mixture is cooled, filtered, and the solid is washed with petroleum ether. The black residue is dissolved in either, any carbonized material is filtered off, and the either is distilled es. Yield,0l55*gm.'of'fl amino pymzine; 80.4% of theory.

Exmpmm 1 ":gm. of crude"2-amino-3-carboxyl -pyrazine in 3 cc. of n-butyl phthalate is heated at 215- 22'O-'C.-untilevolution oiCOz ceases, The reactionmixtureis cooled. 10 "cc. of petroleumether are added. The mixture is'cooled' to C. The solid which formsisfiltered ofi, and washed with petroleum ether. "Yield of z-amino pyrazine, 0678' gm.;'99.3 of theory. This product may be further purified hy dissolving it in 10 cc. of 10% sodium hydroxide and extracting the solution with ether.

EXAMPLEXII 0.50gm. of 2 amino-3 carboxy1" pyrazine l0 cc.:of wateris heated in 'a bomb for '10 hourset 150 C. Excessl30%isodium hydroxide is added, and the mixture is extracted to completion with ether, and the ether extracts are taken to dryness. Yield of 2-amino pyrazine, 65.8% of theory. 7

EXAMPLE .XIII

'The sodium salt'of .2-amino-3-carboxyl pyrazi-helsd'issolved in water. The pH of. the solution is adjusted to about 2 by the addition of hydrochloric acid. The. mixture is heated in'a bomb for 10 'hoursi' at 150 C., extracted with ether, and theether extracts are taken to dryness. Yield of Z-amino pyrazine, about 65.8 ofitheory.

EXAlVEELE XIV Q25 gm. of crude;2 amino 3-carboxy1 pyrazine ererm'xed' with'75 cc. o'f'th'e acetate of diethylene glycol monoethylether and poii'edflunder reflux for 15 "minutes. 1 gm. of decolorizirlg black is 'a'ditledfto theh'otreaction mixture, which is then filtered. while hot, and the filtrate 'is'washed "with about two 5 cc. portionsof hot diethylene glycol monoethylether acetate. 225 'cc. "ofpetroleurn ether are added, and the mixture is chilledto-O C; The crystals are" collected, Washed with petroleum ether, until "free ofjthe acetate of diethylene glycol monoethylet'lier and dried. Yield of 2 ar'riino'pyrazine, 14.0 'gms.;"'8'- .3"%' of theory.

EXAMPLE'XV 1 deems. ofcrude' 2-.amino-3-earhoxy-l.pyrazine are mixed; withi75lcc. of nitrobenzene. and'hoiled ,underrefiuxiorifirniiiutes. 1, gm. of decolorizlug/black is addedltoiihehot reaction mixture, which. is filtered while hot, and the. filtrate ischil-ledto roomtemperature. .300 cc. of petroleum ether are'ad'ded, .with stirring. The mix- "Qure ispermitted tos'tandior about '10 minutes, after whichthe crystalline material is collected, washed 'repeatedlyt with petroleum ether. and dried. Yield. of 'Z amino pyrazine, "15.9 gms.; 93.5% of'theory.

EXAMPLE 8 Examm XVII Onegm. of the sodium-salt of 'Z auiino-3carboxyi pyrazine ismixedwith 10 cc; of-preheated 100% sulfuric acid, and the"mixture-is held 'at Zed-245 C: for 15' minutes. The reaction mixture' is diluted with ice, madealkaline with-30% sodium hydroxide solutionahd extracted with ether. The ether extract 'is evaporated to dryness. Yield of Z-amino pyrazine, 0.46 gm. or 78.3% oftheory.

EXAMPLE XVIII Five gmsof 2-amino-3-carboxyl pyrazine'are mixed with 50 ccfof preheated 100% sulfuric acid." and the mixture is held'at 240-245" C. for 15 minutes, The reaction mixture is diluted with ice; made alkaline witih 30% sodium hydroxide solution and extracted with ether. The ether'extracts are evaporated to dryness. Yield of 2 a1nino-"pyrazine,'3'.08 gms; of theory.

EXAMPLE XEX Five girls. of 2-hydroxy-3-carboxyl pyrazine aremixedwith 1500. of the acetate ofidiethylene glycol monoethylether and boiled under reflux for 10 minutes. The mixture is cooledandBO cc, of petroleum other are added. The crystals are collected and washed with petroleum ether. Yield of' 2-hydroxy pyrazine, 3.0.9'gms.; 90.1% of theory.

EXAMPLE XX Five ems. of 2-amino-3-carboxyl-6-methyl pyrazine'in'50 cc. of 80%-sulfuricacid are heated under reflux at 200C. for ten minutes. 150 ems-of ice are added, followed by-25.0.cc. of-=30% sodium hydroxide. The alkalinized solution is extracted to completion with six 200 cc. portions of ether at 30 C. The'ether is distilled ofi, and the residue is dried. Yield of 2-amino-6-methyl pyrazine, 3.27 gms; 91.8% of theory; M. P; 125- 127 C.

EXAMPLE XXI 2.l5"gms; of 2-amino-5,6-dimethyl-3carboxyl pyrazine are dissolved in 20 cc. of 30%sulfuric acid, and'heated."at'JQE-QOO C. under refiux 'fer 10 minutes. '75 gms. of ice lare'added, followed by cc. .of".30'% sodium hydroxide. The mixture'is extracted -at"30 C. with six 100cc. portions of ether. The ether extracts are takento dryness, :and the residue is dried. Yield .of2- amino-5,6-dimethyl pyrazine, Lfl'gmsq; 93.7%2of theoryyM. P. 14.7-14.8 C.

EXAMPLE XXEI 0.5 gm. of crude 2-;mino-3carboxyl-5,6-di- 'phenyl pyrazine is added-to 1 0 cc. of 80% sulfuric .acid, and the mixture is-refiuXed for 30 minutes. The reaction mixture is cooled- 50 gains. "of 'icezare added, followed by 25 cc. of 30-% sodium hydroxide solution. The insoluble product is filtered oiif; washed several times with 15 sodium hydroxide solution and then with water untilfree fromelkali, and dried invacuo. After one recrystallization from ether, the compound, 2-amino-5;6-diphenyl pyraziite, melts at about 22'J-228C..

Theparenit applications above mentioned; :Serial Nos. 502,967 and 502,969;,.are;two cite. series of applications upon related subject matter concurrently filed by the applicants Weijlard and Tishler, and one instance -:with' another applicant. These concurrently filed applications are as ftollowsz Serial No: -:5'02;965, now abandoned,

reI-ates 7 toithe decarboxylation, heating with sulfuric acid, of 2-amino-3-carboxy-pyrazines and/or Z-hydroxy 3 carboxyl-pyrazines; Serial No. 502,966, new Patent Number 2,447,148, filed August 17, 1948, relates to cleavage of the pyrimidine ring of pyrimidopyrazines b heating the same with an aqueous solution of alkali-metal hydroxide; Serial No. 502,967 relates to the process of Serial No. 502,966 and in addition embraces the recovery of the free amino-carboXy-pyrazines and their decarboxylation; Serial No. 502,968, now abandoned, relates to cleavage of the pyrimidine ring of alloxazine by heating with ammonium hydroxide, followed by acidification and decarboxylation; Serial No. 502,969 relates to the thermal decarboxylation of 2-amino-3-carboxypyrazines and/or 2 hydroxy 3 carboXy-pyrazines; Serial No. 502,970, no abondoned, relates to the pyrimidine-ring cleavage of pyrimidopyrazines by treatment with aqeous alkali-metal hydroxide in excess to form alkalimetal salt of corresponding carboxypyrazines; and Serial No. 502,971, now Patent Number 2,431,896, filed December 2, 1947, relates to cleavage of the pyrimidine ring of pyrimidopyrazines by heating same with concentrated sulfuric acid.

Modifications ma be made in carrying out the present invention without departing from the spirit and scope thereof, and we are to be limited only by theappended claims.

We claim:

1. The process that comprises heating 2-hydroxy-3-carboxyl-pyrazine at a temperature of at least C. in a high boiling indiiferent solvent, and recovering the Z-hydroxy pyrazine thus formed.

2. The process comprising heating under reflux for about 10 minutes 2-hydroxy-3-carboxyl pyrazine in the acetate of diethylene glycol monoethylether, and recovering 2-hydroxy pyrazine.

3. 2-hydroxy pyrazine.

JOHN WEIJLARD. MAX TISHLER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,389,065 Lee et al Nov. 13, 1945 2,396,066 Winnek Mar. 5, 1946 OTHER REFERENCES Maier-Bode, Das Pyridin und seine Deriv-ate, p. 141 (1934 ed.)

Berichte, 67B, pp. 892-908 (1934) Berichte, 70, pp. 761-768 (1937). 

